Internal combustion engines utilize feedback from exhaust gas oxygen sensors to maintain desire air-fuel ratio mixtures during combustion, at least under some conditions. Various types of exhaust gas oxygen sensors may be used, such as linear type sensors (sometimes referred to as UEGO sensors), and switching type sensors (sometimes referred to as EGO, or HEGO, sensors, depending on whether a heater is included).
The inventors herein have recognized that under some conditions, it may be advantageous to utilize a switching type sensor, such as when operating about stoichiometry, as it may be possible to have a more accurate identification of stoichiometry through operating conditions and sensor aging. Further, it may be advantageous to utilize a linear type sensor, such as when operating away from stoichiometry (e.g., lean), as it may be possible to have a more accurate identification of air-fuel ratios over a broader range. However, the additional costs of adding sensors typically forces selection of a single sensor type for any given exhaust location, at least in some systems.
One approach that attempts to use both types of sensor places one type of sensor upstream of a catalyst, and another type of sensor downstream of the catalyst. See, for example, U.S. Pat. No. 6,567,738 and U.S. Pat. No. 5,832,724. However, the inventors herein have recognized that whichever selection is made, each has disadvantages, such as noted above. Further, these disadvantages can be exacerbated when the engine operates in various lean, stoichiometric, and decontamination modes. Specifically, when performing decontamination cycles where some cylinder are operated with an oxygen rich exhaust, and other cylinders are operating with a reductant rich exhaust, degraded temperature control may be encountered (due to air-fuel ratio errors) that can degrade catalyst operation.
The above issue may be addressed by, in one example, a system for a vehicle traveling on the road. The system comprises: a first cylinder; a second cylinder; a linear exhaust gas sensor coupled exclusively to said first cylinder; a switching exhaust gas sensor coupled exclusively to said second cylinder; and a controller configured to perform a decontamination cycle where one of said first cylinder and second cylinder produces a reductant rich exhaust and the other of said first and said second cylinder produces an oxygen rich exhaust, where an air-fuel ratio of one of said first and second cylinder is adjusted in response to said linear sensor.
In this way, it is possible to improve stoichiometric operation and reduce overall system cost since at least one switching type sensor is provided that can provide compensation to both cylinder groups. Further, it is possible to improve lean operation since at least one linear type sensor is provided that can also provide compensation to both cylinder groups. Finally, a decontamination cycle can be accurately controlled using both the linear and switching type sensor, since at least one of the oxygen rich gasses, or reductant rich gasses can be accurately measured via the linear sensor, and thus accurately limit the exothermic reaction (since the reaction will be limited by one of excess oxidants or excess reductants).